Anti-theft device



FIG. 1 is a top right side perspective view of an anti-theft device according to my new design;

FIG. 2 is a front view (the rear view is a mirror image) thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof. 

The ornamental design for an anti-theft device, as shown and described. 